docker: update web image build process and README

- Added a new target "web-build" to streamline the build process for web artifacts.
- Updated "evobgp-web" and "evobgp-web-all" targets to utilize the new "web-build" context.
- Modified Dockerfile to reflect changes in the build stages and context for web artifacts.
- Revised README to clarify the new build process and dependencies.

deploy/docker/docker-bake.hcl

@@ -65,7 +65,7 @@ group "go-images" {
 }
 
 group "web-images" {
-  targets = ["evobgp-web", "evobgp-web-all"]
+  targets = ["web-deps", "web-build", "evobgp-web", "evobgp-web-all"]
 }
 
 # --- Go: go mod download → все cmd/* → birdc (один раз) → runtime-образы ---
@@ -202,13 +202,26 @@ target "web-deps" {
   cache-to   = web-cache-to()
 }
 
-target "evobgp-web" {
+target "web-build" {
   context    = "../.."
   dockerfile = "deploy/docker/evobgp-web/Dockerfile"
+  target     = "build"
   platforms  = ["linux/amd64"]
   contexts = {
     deps = "target:web-deps"
   }
+  cache-from = web-cache-from()
+  cache-to   = web-cache-to()
+}
+
+target "evobgp-web" {
+  context    = "../.."
+  dockerfile = "deploy/docker/evobgp-web/Dockerfile"
+  target     = "web"
+  platforms  = ["linux/amd64"]
+  contexts = {
+    web-artifacts = "target:web-build"
+  }
   args       = { EVOBGP_UPSTREAM = "evobgp-api" }
   cache-from = web-cache-from()
   cache-to   = web-cache-to()
@@ -216,8 +229,16 @@ target "evobgp-web" {
 }
 
 target "evobgp-web-all" {
-  inherits   = ["evobgp-web"]
+  context    = "../.."
+  dockerfile = "deploy/docker/evobgp-web/Dockerfile"
+  target     = "web"
+  platforms  = ["linux/amd64"]
+  contexts = {
+    web-artifacts = "target:web-build"
+  }
   args       = { EVOBGP_UPSTREAM = "evobgp-all" }
+  cache-from = web-cache-from()
+  cache-to   = web-cache-to()
   tags       = image-tags("evobgp-web-all")
 }